This invention relates to liquid skin cleansers. More particularly, this invention relates to liquid skin cleansers comprising surfactants and lather boosters.
The cleaning of skin with surface-active cleaning preparations has become a focus of great interest. Many people wash and scrub their skin with various surface active preparations several times a day. Skin cleansers should cleanse the skin gently, causing little or no irritation, without defatting and drying the skin after frequent routine use. Certain synthetic surfactants are particularly mild. However, a major drawback of mild liquid synthetic surfactant systems when formulated for skin cleansing is poor lather performance. Compared to the highest bar soap standards (bars which are rich in coconut soap and super fatted), these prior art liquid surfactant formulations have either poor lather or poor skin mildness performance. As may be expected the lather performance is a function of the choice of surfactant and its concentration. The conceivable number of liquid surfactant compositions formulated with or without skin feel agents are numerous. Rheological and phase properties exhibited by prototypes vary widely (i.e., thin liquids, gels, thick pastes, solutions, emulsions). The phase stability of prototypes is for the most part acceptable over short time periods, but only a small fraction of them will maintain their original properties and acceptability over an extended period of time.
Optimization of lather as a single variable is a fairly straightforward process. The use of known high sudsing anionic surfactants with lather boosters yields acceptable lather volume. Unfortunately, highest sudsing anionic surfactants are, generally, also highest in skin oil removal and are worst in clinical mildness. Surfactants that are among the mildest with minimal skin oil removal, such as ammonium lauryl ether (12 EO) sulfate (NH.sub.4 AE.sub.12 S) are extremely poor in lather. These two facts make the surfactant selection and the lather boosting optimization process a delicate balancing act.
The ability of relatively small amounts of certain solubilized organic compounds to increase the foaming power of the fatty alkyl sulfates has been recognized for a long time. It is well known, for example, that in sulfating lauryl alcohol with chlorosulfonic acid, the use of excess sulfating agent will result in a product having very poor foam stability, and that the addition of free lauryl alcohol to this product will restore the foaming power. Lauryl alcohol is, accordingly, a foam-promoting builder for lauryl sulfate, and the high-foaming grades of commercial lauryl sulfates have always, since the first time produced in quantity, contained a small portion of lauryl alcohol. This proportion usually varies between 2% and 10% of the lauryl sulfate present and the precise content of lauryl alcohol is frequently a purchasing specification for lauryl sulfate detergents.
Lauryl alcohol and other members of the fatty alcohol series are also foam builders for certain other detergents, although they are reported not to be effective when used with the alkyl aromatic sulfonates. In general, the foam-building effect is highly specific, and materials which build the foam of one type of detergent may have little or no effect on another type. Another important characteristic of foam builders is that their effect varies considerably with the concentration. An excessive amount of a foam builder, relative to the amount of surfactant present, may actually have a foam-suppressing effect. The fatty monoethanolamides have been claimed and used commercially as foam builders for fatty alkyl sulfates. In practice lauryl or coconut monoethanolamide is used since they are much more effective than the higher members of the series.
The fatty diethanolamides have been favored as foam builders for the alkylarylsulfonates (British Pat. No. 693,063 to Colgate-Palmolive Peet Company). Coconut-oil fatty diethanolamide is said to be particularly effective, and has been widely used as a foam builder. This latter product is known to contain besides the fatty diethanolamide, some free fatty acid and amino fatty esters (H. L. Sanders and E. L. Knaggs, Soap and Sanit. Chemicals,, 29, No. 6, 45-8 (1953)). The fatty alkylol amides have also been used with soaps to promote and stabilize foams (Zussman et al., Soap and Sanit. Chemicals, 26, No. 4, 37-40, 141 (1950)).
U.S. Pat. No. 2,879,231, Allen et al., issued Mar. 24, 1959, relates to shampoos which may contain fatty acids and amides. E.g., in U.S. Pat. No. 4,151,105, J. R. O'Roark, issued Apr. 24, 1979. O'Roark's solid bar soap, however, requires from 10-30% paraffin, 5-15% starch and 10-30% dextrin, which is undesirable for liquid skin cleansers. Coconut-oil fatty acid is used to promote the plasticity and improved sudsing in a low pH synthetic bar soap. The coconut-oil fatty acid is used with lauric diethanolamide to supplement the coconut fatty acid.
In short, the rather stringent requirements for skin cleansers limit the choice of surface-active agents, and final formulations represent some degree of compromise. Mildness is often obtained at the expense of effective cleaning, or lathering may be sacrificed for either mildness, product stability, or both.
The present invention offers a valuable combination of desirable properties to liquid skin-cleaning formulations.
Therefore, one object of this invention is the development of liquid skin cleaning compositions which exhibit mild surface-acting and good lathering properties.
Another object of the present invention is the development of low cost liquid skin cleansers.
Other objects will become apparent from the detailed description below.